1. Field of the Invention
The embodiments disclosed herein and the invention as claimed relate to a valve assembly to prevent the flow of fluids past the assembly, to systems incorporating such assembly, and to methods for using the assembly. In one preferred embodiment, the valve assembly is incorporated into a system of selectively operable frac sleeves for use in completing a well for oil, gas or other hydrocarbons.
2. Background
In hydrocarbon wells, tools incorporating valve assemblies having an engaging element, such as a ball or dart, and a receiving element, such as a ball seat or dart seat, have been used for a number of different operations. Such valve assemblies prevent the flow of fluid past the assembly and, with the application of a desired pressure, a well operator can actuate one or more tools associated with the assembly.
One use for such remotely operated valve assemblies is in fracturing (or “fracing”), a technique used by well operators to create and/or extend one or more cracks, called “fractures” from the wellbore deeper into the surrounding formation in order to improve the flow of formation fluids into the wellbore. Fracing is typically accomplished by injecting fluids from the surface through the wellbore and into the formation at high pressure to create the fractures and to force them to both open wider and to extend further. In many case, the injected fluids contain a granular material, such as sand, which functions to hold the fracture open after the fluid pressure is reduced.
Fracing multiple-stage production wells requires selective actuation of downhole tools, such as fracing sleeves, to control fluid flow from the tubing string to the formation. For example, U.S. Published Application No. 2008/0302538, entitled Cemented Open Hole Selective Fracing System and which is incorporated by reference herein, describes embodiments which incorporate a shifting tool for selectively actuating a fracing sleeve.
That same application also describes a system using multiple valve assemblies which incorporate ball-and-seat seals, each having a differently-sized ball seat and corresponding ball. Frac valves connected to ball-and-seat arrangements do not require the running of a shifting tool thousands of feet into the tubing string and are simpler to actuate than frac valves requiring such shifting tools. Such ball-and-seat arrangements are operated by placing an appropriately sized ball into the well bore and bringing the ball into contact with a corresponding ball seat. The ball engages on a section of the ball seat to block the flow of fluids past the valve assembly. Application of pressure to the valve assembly causes the valve assembly to “shift,” opening the frac sleeve to the surrounding the formation.
Some valve assemblies are selected for tool actuation by the size of ball introduced into the well. If the well or tubing string contains multiple ball seats, the ball must be small enough that it will not seal against any of the ball seats it encounters prior to reaching the desired ball seat. For this reason, the smallest ball to be used for the planned operation is the first ball placed into the well or tubing and the smallest ball seat is positioned in the well or tubing the furthest from the wellhead. Thus, these valve assemblies limit the number of valves that can be used in a given tubing string because each ball size is only able to actuate a single valve. Further, systems using these valve assemblies require each ball to be at least 0.125 inches larger than the immediately preceding ball. Therefore, the size of the liner restricts the number of valve assemblies with differently-sized ball seats. In other words, because a ball must be larger than its corresponding ball seat and smaller than the ball seats of all upwell valves, each ball can only seal against a single ball seat and, if desired, actuate one tool.
The embodiments disclosed herein relate to an alternative for sequentially engaging multiple receiving elements with a single engaging element and, where desired, actuating tools associated with the valve assembly. One embodiment of the present invention allows multiple balls of the same size to actuate tools in sequential stages.
In fracing operations, the embodiments of the valve assembly disclosed herein, enable an increase in the number of stages that can be performed using ball-and-seat or similar valve assemblies. The increase in frac stages can increase the total number of sleeves that can be opened for fracture treatments, reduce the number of frac valves that are opened for each stage, or both. Further, if additional stages are not needed, the invention valve assembly such as those disclosed herein can be used to limit the valve assemblies used to those having larger diameter balls and ball seats, thus enlarging the fluid path in the wellbore or tubing and improving the flow of fluids form the wellhead to the formation to be treated.
In an alternate aspect, valve assemblies such as those disclosed herein are useful to perform multiple pressure cycles on installed tubing by using a single engaging element sequentially on multiple receiving elements or by sequential engagement of a single receiving element with multiple engaging elements.